Noncoordinating anions, in which boron connects to perfluorinated phenyl ligands that increase the anion's lability and stability with respect to un-wanted reactions with the metal cation complexes, are known. (U.S. Pat. No. 5,198,401). Examples of these include tetrakis(pentafluorophenyl)borate, [B(PfP)4]− or [B(C6F5)4]−. Suitable aryl radicals other than phenyl radicals, e.g. naphthyl and anthracenyl, are described. U.S. Pat. No. 5,296,433 describes borane complexes comprising tris(pentafluorophenyl)borane and specific complexing compounds. These complexes polymerize higher molecular weight polymers when used with metallocene catalysts apparently due to their increased monomer or monomer solution solubility. WO 97/29845 describes preparing perfluorobiphenyl borane and using this Lewis acid to prepare and stabilize active olefin-polymerization catalysts. Apparently, these cocatalysts are less coordinating than tris(perfluorophenyl)boron, B(C6F5)3 and yield higher catalytic activities. That document describes cocatalysts with the formula BR′″ where B is boron, and R′ and R″ represent one or more fluorinated biphenyl's or other polycyclic groups, such as naphthyl, anthryl or fluorenyl.
Olefin solution-polymerization processes are generally conducted in aliphatic solvents to maintain reaction temperature and solvate the polymer product. But aryl-group-containing activators dissolve poorly in such solvents. Typically, activators are introduced in toluene or other aryl solvents. Thus, toluene contaminates aliphatic-solvent-based processes. It must be removed because it tends to harm process efficiency. Moreover, aryl-based solvents may be unhealthful in large-scale polymerization and in the resulting polymer. Alternatively, slurries can transport the activators, but that complicates their use and increases plant design costs and operation costs. Low solubility problems are exacerbated when processes involve a low temperature stage, e.g. adiabatic processes run in colder climates. Additionally, separating the solvent or counteracting its build up in the recycle system presents other problems that counter industrial goals. One goal of those is to maintain high polymer molecular weights while operating at high reaction temperatures and high polymer production rates. Therefore, industry desires higher aliphatic solubility for cocatalyst activators.
U.S. Pat. No. 5,502,017 discloses metallocene olefin-polymerization catalysts that contain a weakly coordinating anion based on boron substituted with halogenated aryl or silylallyl substituents, such as tert-butyl-dimethyl-silyl. Apparently, this substitution increases the metallocene salt's solubility and thermal stability. Examples 3-5 describes the synthesis of and polymerization with the cocatalyst: triphenylcarbenium tetrakis (4-dimethyl-t-butylsilyl-2,3,5,6-tetrafluorophenyl)borate.
Thus, a need exists for cocatalyst compounds that improve solution polymerization economics and that provide alternative activators for olefin-polymerization catalyst systems.